Conference Proceedings Paper
Impacts of Organic Sources on the Ozone Depletion
Events in Arctic Spring
Zhaohuan Liu and Le Cao *
Published: 15 July 2016
Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration,
Nanjing University of Information Science and Technology, Nanjing 210044, China
* Correspondence: [email protected]
Abstract: Impacts of atmospheric halogens on the ozone depletion events (ODEs) in polar boundary
layer have been under investigation since the discovery of negative correlation between atmospheric
ozone and bromine. By simulating an ODE in a box model KINAL, this study focuses on the
influence of natural organic sources on the ozone depletion. An estimation of bromine flux from
Arctic plantation is given as 6.3 × 106 molec. Br/(cm2 ·s). Since there exists huge fluctuation
in the flux, the bromine input is set to be adjustable, by which the impact of Arctic biological
behavior on the tropospheric ozone can be predicted. Meanwhile, another nitrogen flux emitted from
plants is also included in the model as the plants release considerable amount of nitrogen into the
atmosphere, which alters the process of the ozone depletion. Different from the Br flux, the nitrogen
flux implemented in the model remains relatively stable around 1 × 108 molec. NO/(cm2 ·s).
The simulation results indicate that the type of the Br flux plays a relatively important role in
the depletion of ozone. An average level of Br input may cause approximately a 1.0 day antedate to
the ODE. In contrast to that, NO exerts minor impact on the ozone concentration, but an obvious
force to the mixing ratio of Br species.
Keywords: ozone depletion; arctic; organic source; bromine flux
1. Introduction
In the boundary layer of polar regions, an ozone depletion event (ODE) is often observed in the
early spring when sun rises [1]. During the observations in Barrow, Alaska [2], a sudden drop in ozone
concentration is caught. In later observations, it is found that there exists a negative correlation between
ozone and halogens, especially bromine in the boundary layer [3]. Similar tropospheric ODEs and
the corresponding bromine accumulations have been confirmed by a series of observations in Arctic
and Antarctic regions [4–10]. These observations also found sudden releases in halogens during Arctic
ODEs, which are considered to be related to a catalytic cycle containing halogens, especially bromine
whose ozone depleting effect is measured 45 times of chlorine [11]. The catalytic cycle mechanism
can be described as a series of chemical reactions. With the reaction rates and the initial atmospheric
composition given, the temporal evolution of any specific gaseous species can be obtained after a
numerical analysis.
An ODE can be divided into three periods: the induction stage, the depletion stage and the end
stage according to the temporal evolution of tracking gases [12]. In the induction stage, ozone is hardly
consumed, with a depleting rate lower than 0.1 ppb/h. During the induction stage, the major reactions
taking place are the transformation of inert bromine to active gaseous BrO and HOBr at the saline
surface. Physical structure of the ice/snow surface has a strong impact on the duration of the induction
stage, as rough surface provides more space for halogen recycling heterogeneous reactions. In the
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
second period named depletion stage, ozone is rapidly consumed at a rate higher than 0.1 ppb/h.
As the mixing ratio of HOBr increases during this period, a burst emission of brominated species from
saline surface is observed, resulting in a rapid growth of bromine in the air. This abnormal burst of
atmospheric bromine is the so-called “bromine explosion”. When ozone concentration drops to 10%
of its original value, it is considered that the depletion stage is over and the last period of the whole
ozone depletion, the end stage, begins. During the end stage, as mixing ratio of HOBr reaches a peak,
ozone continues to deplete to its minimum value, which is usually lower than 1ppb. After that, HOBr
is rapidly consumed while molecular Br becomes the major bromine species in the boundary layer.
Br is later transformed into HBr by organic reactions.
Numerical models with different physical dimensions have been applied to investigate the ozone
depleting and halogen recycling processes. 0-D models, or namely box models were first used in 1990s.
In a box model research [13], the Br2 producing reaction:
HOBr(aq) + H+ + Br− −−−−→ Br2 (aq) + H2 O
(R1)
is proposed. After switching off reaction (R1), model simulation shows that little ozone is consumed
within 4 days, indicating that the aerosol phase production of Br2 is essential for ODEs. After that,
modeling results of a steady-state model, BM, is compared to the observations [14,15], showing a
significant impact of bromine chemistry on the mixing ratios of RO2 +HO2 and OH. Afterwards,
a modified version of the photochemical box model MOCCA [16] adapted to polar conditions is
developed, in order to investigate Arctic ODEs. Under this modified model MoccaIce [17], organic
sources are initially prescribed. By analyzing the chemistry in Arctic ODEs by using MoccaIce, the
rate of reactions between Br and C2 H2 or C2 H4 is found critical for the loss of bromide and the ozone
budget in the troposphere. Role of iodine chemistry is also studied at the same time.
1-D models are first presented to inquire the relative importance of sea salt aerosols and fresh sea
ice surface on the ozone destruction [18]. In 1-D models, mass transportation between vertical layers
at different heights is considered. Source strengths of bromine and iodine required for sustaining
the vertical structure of BrO and IO observed are invested by developing THAMO [19], which is a
1-D chemical transport model. In a comprehensive model study on ODEs, special attention is paid
to the cloud microphysics by using a 1-D Lagrangian-mode boundary layer model MISTRA [20].
After modification, MISTRA was applied on the investigation of frost-flower derived aerosols, open
leads and re-release processes on the snowpack during ODEs [21]. It is found that the recycling process
on snow is the most important process for the existence of high-level bromine in the polar boundary
layer. By coupling a snow module to MISTRA, a new model named MISTRA-SNOW is developed [22].
Studies on the basis of MISTRA-SNOW identified the role of in-snow photochemistry, indicating that
the snowpack is able to provide adequate reactive bromine to sustain the BrO level observed [23].
In order to address the influence of reactive bromine released by the snowpack on the ozone loss
in the polar boundary layer, a 1-D physicochemical model PHANTAS is developed, in which HOBr
molecules are assumed vertically transported through the boundary layer and the snowpack. It is
found that in the top layers and deeper layers of the snowpack, bromine release is driven by different
mechanisms [24].
3-D model studies of the tropospheric ODEs in polar regions started from a regional chemistry
transport model RCTM [25]. The correlation coefficient between observed and model-predicted ozone
temporal variations at different sites are found above 0.5. By adding a detailed bromine chemistry
scheme to a global 3-D tropospheric model considering both local chemistry and long-range air
transportation, p-TOMCAT, lifetime and vertical profile of BrO are investigated [26]. Comparison with
observations has proved its capability to simulate the high bromine level during the bromine explosion
events. A global 3-D chemistry and transportation model GEM-AQ/Arctic is applied to investigate
the spatial structure and time series of ozone and BrO in the Arctic boundary layer in spring [27].
Highly salt concentrated aerosols derived from the frost flowers assumed as the only halogen source
2
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
in the troposphere, the air chemistry, the air temperature, atmospheric circulation and long-range
transportation of pollutants are found to make great contribution to the polar ODEs in spring.
In the model studies mentioned above, the fact has been revealed that a comparatively low amount
of bromine may lead to a significant enhancement to ozone depletion. Thus, any possible source of
bromine should be concerned. Studies have shown that snow/ice surface emission is one of the major
bromine sources, and some other inorganic sources have also been found. Snowpack with accumulated
sea-salt particles is possibly the primary source of bromine in Arctic, which provides adequate bromine
and surface area for the heterogeneous halogen recycling [28]. Existence of frost flowers is suggested
to propose the formation of CaCO3 -lack particle in the air, leading to the acidification of SO2 and NO2 ,
which may accelerate the acid-catalyzed bromine explosion process [29]. Blowing snow is estimated
to contribute 8% of the ozone loss in the polar spring [30]. However, the knowledge about organic
halogen sources, which consist of natural and artificial releases of halogens, is still lacking. Respiration
and degradation of plants, excrement of polar animals make up most proportion of the natural source,
while artificial source mainly consists of biomass burning, shipping traffic and bromine-containing
petrochemical organic products transportation. By adding halogen releases from some of these sources
into a numerical model under study, impact of organic sources can be identified by comparing the
results before and after the implementation of the specific sources.
Among the few Arctic plantations, macro-algae and moss are the most widespread species.
Bromine produced by macro-algae is mainly concentrated in the form of CHBr3 , while a relatively
small amount of CH2 Br2 also exists.
Due to the weak human activity inside the Arctic Circle, release from artificial sources is mainly
considered as long-range transportation, which cannot be included in a 0-D model.
The main objectives of this research are listed below:
1.
2.
3.
Analyze an ozone depletion numerically, estimate the input of different organic sources, and
discuss the impact of specific organic sources on the ODE by adding them into a box model.
By adjusting flux input from different potential sources, predict the impact on the tropospheric
ozone from biosphere behavior.
After advancing the box model with extra species and reactions, study the role of organic sources
in releasing NOx species to enhance ODEs.
2. Model Description
The catalytic cycle considered in the model consists of a homogeneous reaction system which can
be described as a differential equation:
dc
= f (c, k) + F
dt
(1)
where c stands for the species concentration vector, k denotes the reaction rate vector, and F represents
the flux vector from the surface. Equation (1) is solved by using the box model KINAL [31], which is a
FORTRAN program developed to solve the differential equation with a fourth-order semi-implicit
Runge-Kutta method. The gaseous species and reactions included in KINAL can be found in [12],
together with the reaction rates under p = 1 atm. With a given initial condition c|t=0 = c0 , known
reantion rate vector k and flux data F, the species concentration at any time can be solved by KINAL.
2.1. Inorganic Sources
As the horizontal transportation is not considered in the present box model, it is assumed
that emission from ice/snow surface and aerosol surface are the only inorganic halogen sources,
the dominate bromine-releasing reactions are the heterogeneous reactions:
aerosols
HOBr + HBr −−−−→ Br2 + H2 O
3
(R2)
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
ice/snow
HOBr + H+ + Br− −−−−−→ Br2 + H2 O
(R3)
The Br2 production rate of (R2) is given as below.
d
d
[Br2 ] = − [HOBr] = kR2 [HOBr]
dt
dt
−1
a
4
kR2 =
+
αeff
Dg
νtherm γ
(2)
(3)
a/Dg represents the molecular diffusion limit, where a is the aerosol radius and Dg is the molecular
diffusivity in the gas phase.
r γ is the uptake coefficient of HOBr on sea salt aerosols. Mean molecular
8RT
speed νtherm is defined as
, where MHOBr is the molar mass of HOBr. R is the universal gas
πMHOBr
constant, and T is the absolute temperature. The surface-volume coefficient αeff is the ratio of total
aerosol surface Aaerosol and the total volume V:
αeff =
Aaerosol
V
(4)
It is assumed that a = 0.45 µm, Dg =0.2 cm2 ·s−1 in the present research; For gaseous HOBr at mixing
ratio of 10 ppt, γ = 0.12; Given that aerosol particles are uniformly distriuted, calculation provides a
typical αeff value of 10−5 cm−1 . Thus, the reaction rate of (R2) is estimated as kR2 = 6.14 × 10−4 s−1 for
10 ppt of HOBr.
Likely, for (R3) occurring at ice/snow surfaces,
kR3 [HOBr] = −
d
[HOBr] = kd [HOBr]
dt
(5)
The deposition rate constant kd is defined as:
kd =
νd
β
Lmix
(6)
where νd is the deposition velocity at ice/snow surfaces, and Lmix is the typical height of a stable
mixing layer, while β is the reactive surface ratio coefficient, defined as the ratio of reactive surface
area and the flat surface area.
A typical polar mixing layer height is believed to reside in a range from near zero to over
1000 m [32]. Following former researches [12,33], Lmix is assumed as 200 m, where νd estimated as
0.605 cm·s−1 . β is determined by the physical structure of the surface, varying from 1 to 103 . In the
present research, β is set as 1.
2.2. Organic Sources
Halogens from organic sources are then added into KINAL as follows.
2.2.1. Macro-Algaes
Macro-algal bromine exists mainly in the form of bromine-substituted methanes (CHBr3 , CH2 Br2 ,
CH3 Br). Macro-algaes produce around 70% of the world’s bromoform [34]. Production rate of CHBr3 ,
CH2 Br2 and CH3 Br are estimated 1.7 × 102 , 2.8 and 0.1 Gg/yr respectively at global scale, which is
equivalent to 1 × 109 mol Br/yr [35], or 5.3 × 106 molec. Br/(cm2 ·s) after spatial average.
4
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
Laboratory researches suggest that the emission rate of macro-algae ranges around 124–5434 ng
CHBr3 /(g dry weight·h), and emission rate in darkness is about half of that in the light [36]. Peak density
of macro-algal biomass in Arctic is observed in mid-May, ranging within 400–600 g dwt/m2 [36].
Growth rate of the biomass is measured to range from 10 to 30 g dwt/(m2 ·d), limited by the light
condition. For an ODE taking place in early spring, the biomass density of macro-algaes can be assumed
around 300 g dwt/m2 . Thus, the overall estimation of macro-algal bromine production rate can be given
as 3 × 108 –1 × 1010 molec. Br/(cm2 ·s).
The bromine-substituted methane species take part in the reaction mechanism through
reactions (R4) and (R5) as follows [34].
CHBr3 + H2 O −−−−→ CH2 Br2 + HOBr
(R4)
Br2 + H2 O ←−−−−→ HOBr + H+ + Br−
(R5)
The bromine hydrolysis reaction (R5) is promoted to produce HOBr under the alkalescent seawater
condition [37]. Although bromine-substituted methane is not contained in the recent KINAL model,
the ozone depleting effect can be considered in the form of HOBr release. Most of the released HOBr is
consumed by reactions with dissolved organic matter (DOM). Taking the assumption that 99% of HOBr
react with DOM [38], the remaining 1% can cause an area-normalized emission of 0.07–3.2 nmol/(m2 ·h),
or 1.2 × 105 –5.4 × 106 molec./(cm2 ·s), which matches the global estimation well.
However, other researches indicate that the primary Br emission is Br2 and BrCl release, which
account for more than 40% of the total bromine emission [38]. According to reaction (R5), taking the
HOBr source assumption, the simulation of ozone depletion should be more rapid than the reality,
for unit amount of HOBr causes double amount of reactive bromine in the air.
Since there is no precise evaluation about Br releases, different proportions of plant-releasing
HOBr and Br2 are examined, while the BrCl emission is ignored.
2.2.2. Moss and Other Polar Plants
On the tundra at lower latitudes in the Arctic region, there is a larger variety of vegetation.
Aboveground live biomass provided by 6 individual functional types (mosses, lichens, forbs, sedges,
deciduous shrubs and evergreen shrubs) are generated according to field data [39]. The spatial mean
value of the total biomass field is estimated 694 g/m2 . Halogens released from shrubs does not
play an important role in the ODE for its low producing rate [40]. Mosses and lichens are the major
bromine-releasing plant types, whose biomass density remains stable under global warming [41].
Spatial averaged live biomass of mosses and lichens are estimated 300 and 50 g dwt/m2 respectively.
Assuming that mosses and lichens have equivalent capability of releasing bromine as macro-algae
species, the flux from tundra landscape can be set as 6.18 × 106 molec./(cm2 ·s).
Considering the polar area is a 2.1 × 107 km2 spherical crown within the Arctic Circle, 60% of
which covered by ocean, while 5.05 × 106 km2 of the land part can be referred to as vegetated [42].
After all, bromine from the plant source can be estimated as approximately 6.3 × 106 molec. Br/(cm2 ·s)
by spatial mean.
The initial mixing ratios of different gaseous species are listed in Table 1; Emission fluxes from
inorganic ice/snow surface source and organic sources are listed in Table 2. Species not listed in Table 1
have a mixing ratio of 0.
5
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
Table 1. Initial mixing ratio of trace gaseous species in the polar boundary layer [12].
Species
Mixing Ratio
O3
Br2
HBr
CH4
CO2
CO
HCHO
CH3 CHO
C2 H6
C2 H4
C2 H2
C3 H8
H2 O
40 ppb
0.3 ppt
0.01 ppt
1.9 ppm
371 ppm
132 ppb
100 ppt
100 ppt
2.5 ppb
100 ppt
600 ppt
1.2 ppb
800 ppm
Table 2. Flux rates from different sources.
Flux Rates [molec./(cm2 ·s)]
Species
Inorganic Sources [12]
H2 O2
HCHO
HOBr and Br2
Natural Organic Sources
108
1.0 ×
6.0 × 107
6.3 × 106 molecules of Br (average)
2.3. Model Implementation—Adding Nitrogen
Plants are the major organic bromine source, while their capability of emitting nitrogen-related
species is also notable. KINAL is improved by adding nitrogen species and relating reactions into it, in
order to get better simulating results. The major nitrogen species emitted by plants are NO and N2 O,
among which N2 O does not participate in the ozone depleting cycle.
NO emission from macro-algae reaches a steady rate of 0.5–1 nmol/(mg chlorophyll·h) after
illumination [43]. Observations of chlorophyll density varies around 6–18 mg/m2 [44]. Thus,
NO emission from macro-algaes ranges within 5 × 107 –3 × 108 molec./(cm2 ·s). For rough estimation,
an emission of 1 × 108 molec./(cm2 ·s) is assumed. The initial mixing ratio and flux rates of nitrogen
species are listed in Table 3.
Table 3. Initial mixing ratios and flux rates of nitrogen species added into KINAL.
Species
Flux Rates [molec./(cm2 ·s)]
Initial Mixing Ratio [12]
NO
NO2
HONO
Inorganic Sources [12]
Organic Sources
1.6 × 107
1.6 × 107
1.6 × 107
1 × 108
5 ppt
10 ppt
0
3. Results and Discussion
3.1. Bromine Model
Simulation results of adding organic bromine sources are shown in Figure 1. In the first few
days of the induction stage, the major change in bromine species is the growth of HOBr and BrO.
With the increase in HOBr, large amount of inert bromine in the ice/snow surface is emitted through
heterogeneous reactions, which causes a rapid increase in the total atmospheric bromine. After the
induction stage, drop in ozone concentration results in a decline in the oxidability of atmosphere, and
6
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
the reducing gases such as HBr and Br start to grow vigorously. At the end of the depletion stage,
BrO and HOBr reach their peak values of about 60 and 90 ppt, and then quickly deplete. Meanwhile,
Br becomes the major atmospheric bromine, reaching a peak of more than 150 ppt. In the end stage,
Br is consumed by aldehydes in the troposphere [12], leaving high concentration of HBr in the air.
150
BrO
100
HBr
O
HOBr
10
50
Br
total
0
0
2
4
6
8
0
10
Br,BrO,HBr,HOBr,Br
3
Br
20
3
[ppb]
O
total
200
30
[ppt]
250
40
Time [day]
(a)
150
BrO
100
HBr
O
HOBr
10
50
Br
total
0
0
2
4
6
8
0
10
Br,BrO,HBr,HOBr,Br
3
Br
20
3
[ppb]
O
total
200
30
[ppt]
250
40
Time [day]
(b)
20
150
BrO
100
HBr
O
HOBr
10
50
Br
total
0
0
2
4
6
8
0
10
Br,BrO,HBr,HOBr,Br
3
Br
3
[ppb]
O
total
200
30
[ppt]
250
40
Time [day]
(c)
Figure 1. Simulated temporal evolution of bromine species and ozone when there exists: (a) only
inorganic sources; (b) norganic and vegetal HOBr source; (c) inorganic and vegetal Br2 source.
Existence of direct bromine input causes significant impact on the ozone depletion, as shown in
Figure 1b,c. After adding organic sources, ozone depletion is greatly fastened, while peaks of HOBr, Br
and BrO are also antedated. However, time for these bromine-related gases to completely disappear
in the boundary layer from their peaks is not reduced. Period from Br peak to Br depletion remains
about 2.0 days. As shown in Table 4, for an average level of either HOBr and Br2 source input, the
induction stage is reduced for more than 1 day, while duration of the depletion stage lasts for around
1.0 day, not obviously influenced. Type of the source input does not show much importance. Figure 2
7
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
shows the difference caused by source type. When Br2 makes up 90% of the total bromine emission
(the highest Br2 ratio reported), simulation shows no obvious difference against the situation when Br2
accounts for 40% of the totality.
Table 4. Peak time and values of gaseous species, and stage beginning time under average level of
organic source input.
Peak Time (day)
HOBr
Br
BrO
HOBr
Br
BrO
5.4
4.1
4.2
5.6
4.4
4.4
5.3
4.0
4.1
90
83
87
165
154
165
55
56
54
Depletion Stage (day)
End Stage (day)
4.4
3.2
3.2
5.4
4.1
4.2
3
150
Br
20
HBr
100
HOBr
O
3
[ppb]
O
total
200
30
40% Br
2
10
50
90% Br
2
0
2
[ppt]
250
40
4
6
0
Br,BrO,HBr,HOBr,Br
Inorganic Only
Vegetal [HOBr]
Vegetal [BR2 ]
Peak Value (ppt)
Time [day]
Figure 2. imulated temporal evolution of O3 , Br, HBr and HOBr with different ratio of Br2 input when
there is an average input of bromine. Dash lines represent high Br2 ratio (90%).
In KINAL, HOBr acts as a reactant in three reactions: HOBr + hν, HOBr + HBr, and
HOBr + H+ + Br− . The latter two reactions double the bromine input to the boundary layer. If they are
the dominant reactions taking place in the induction stage, the Br2 proportion should have significant
impact on the behavior of ozone. Because of the existence of:
HOBr + hν −−−−→ OH + Br
(R6)
and its relatively high rate, most of directly released HOBr is consumed through photolysis process
in the first few days of an ODE. After gaseous HOBr is accumulated after the induction stage,
heterogeneous reactions (HOBr + HBr) and (HOBr + H+ + Br− ) become the major sink of HOBr.
Due to the weak impact of bromine source type on the whole event, assumption is taken in the
present research that 60% of bromine released from plants is concentrated in HOBr.
Since the natural source emission fluctuates greatly around the mean valus, an input adjustment
is conducted in order to study ODEs under different levels of bromine release. As shown in Figure 3,
the ozone depleting rate at the depletion stage remain around a fixed value under different source
intensities. As source input increases, the induction stage is shortened, while duration of the depletion
stage is not significantly influenced. However, the induction stage reduction is not limitless. For a
higher source intensity, the shortening effect on the induction stage becomes slighter.
8
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
40
30
Natural Source Intensity
0.25
0.50
O
3
[ppb]
0.00 (Inorganic Only)
20
0.75
10
1.00
[O ]=4.0ppb
1.25
0
2
3
3
4
5
Time [day]
Figure 3. Simulated temporal evolution of O3 under different intensity of natural sources. Natural
source intensity indicates the relative ratio of natural source emission and its mean value.
3.2. Nitrogen Implementation
After the addition of nitrogen (N), enhancing effect of organic source on the ozone depletion
is confirmed, as shown in Figure 4. In the induction stage and the depletion stage, behavior of the
trace gases are not significantly influenced by the nitrogen input. Large amount of NO input from
organic sources causes a lesser enhancement to ozone depletion, which leads to a 0.2 day antedate to
the induction stage. As shown in Table 5, due to the 0.2 day speeding effect, the peaks listed are all put
forward at the same extent.
200
total
3
150
BrO
20
HBr
100
HOBr
O
3
[ppb]
Br
Br
10
0
total
0
2
50
4
6
8
0
10
Br,BrO,HBr,HOBr,Br
O
30
[ppt]
250
40
Time [day]
(a)
150
BrO
100
HBr
O
HOBr
10
50
Br
total
0
0
2
4
6
Time [day]
(b)
Figure 4. Cont.
9
8
0
10
Br,BrO,HBr,HOBr,Br
3
Br
20
3
[ppb]
O
total
200
30
[ppt]
250
40
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
150
BrO
100
HBr
O
HOBr
10
50
Br
total
0
0
2
4
6
0
10
8
Br,BrO,HBr,HOBr,Br
3
Br
20
3
[ppb]
O
total
200
30
[ppt]
250
40
Time [day]
(c)
Figure 4. Simulate temporal evolution of bromine species and ozone when there exists: (a) inorganic
sources only; (b) inorganic sources and organic bromine sources; (c) inorganic sources and complete
organic source.
Table 5. Peak time and values of specific events under different organic source input, as the organic
source consists of average level of Br and N input at the same time.
Br Peak
HOBr Peak
Brtotal Stability
Time (day)
Br Only
Br and N
4.6
4.4
4.4
4.2
4.6
4.4
Value (ppt)
Br Only
Br and N
158
164
85
88
185
192
As the model implementation consists of heterogeneous reactions:
aerosols
BrONO2 + H2 O −−−−→ HOBr + HNO3
ice/snow
BrONO2 + H2 O −−−−−→ HOBr + HNO3
(R7)
(R8)
Addition of nitrogen species provides extra approaches to release bromine from the inert phase,
resulting in extra atmospheric bromine, which causes direct enhancement to the ODE. On the
other hand, NO has great potential to form tropospheric ozone [45], which may decelerate the
ozone depletion. In the present research, the total effects of organic NO emission makes the ODE
slightly enhanced.
Simulation of N species are shown in Figure 5. PAN and HONO are the major nitrogen compounds
in the boundary layer. PAN is the major nitrogen species after the induction stage, whose mixing ratio
keeps increasing undil day 5.1. After that, PAN is slowly consumed, dropping from the 75 ppt peak.
Rather than ozone, the bromine vestige left in the boundary layer after the ODE is more influenced
by the N input. According to Figure 4c, a declining trend is expected in HBr. At the end of simulation,
mixing ratio of HBr drops to approximately 120 ppt. On the contrary, former-depleted Br is accumulated
again, fluctuating around 15 ppt.
Temporal evolution of bromine species in the ODE is shown in Figure 6. Mixing ratio of BrNO2
keeps increasing after day 4, reaching 70 ppt at the end of simulation. Forming rate of BrNO2 and
consuming rate of HBr are roughly equivalent, indicating that transformation from HBr to BrNO2 is
an important reaction taking place in the end stage.
As shown in Figure 7, form if gaseous species in the boundary layer differs significantly as NO
input from organic sources changes. Increase in NO source intensity enhances the transformation from
HBr to BrNO2 . When there is a NO input of 1.5 × 108 molec./(cm2 ·s), which can be easily obtained
with warm weather and temperature condition, BrNO2 takes almost equal proportion in the total
10
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
bromine as HBr. It can be predicted that BrNO2 should become the major atmospheric bromine species
after the ODE for a higher NO source intensity caused by climate change or ocean eutrophication.
O
30
3
PAN
[ppb]
NO
NO
20
50
2
O
3
HONO
10
0
0
2
4
6
8
Nitrogen Species [ppt]
100
40
0
10
Time [day]
Figure 5. Simulated temporal evolution of major atmospheric nitrogen species during the ODE under
average Br and N input of organic sources. PAN stands for peroxyacetyl nitrate (CH3 CO3 NO2 ).
[ppt]
2
HBr
2
Br ,BrONO
200
2
BrO
BrONO
BrNO
1
0
150
HOBr
2
100
2
2
50
0
2
4
6
8
0
10
2
Br
3
Br,BrO,HBr,HOBr,BrNO
Br
[ppt]
250
4
Time [day]
Figure 6. Simulated temporal evolution of bromine species under inorganic and organic sources after
adding N to the model.
200
Natural Source Intensity
2
Br ,BrONO
2
[ppt]
0.5
150
1.0
1.5
100
HBr
BrNO
2
50
0
2
4
6
8
10
Time [day]
Figure 7. Simulated temporal evolution of HBr and BrNO2 under different NO natural source intensity.
Natural source intensity indicates the relative ratio of natural source emission and its mean value.
4. Conclusions
Existence of the organic source addresses significant impact on Arctic ODEs. The major input of
the local organic source is flux from plants, while other inputs are not considered in the present model.
Flux from plants mainly consists of emission from macro-algaes, tundra-based mosses and lichens,
while minor contribution is made by grasses and shrubs. In the present research, fluxes from organic
11
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
sources are divided into two parts: the bromine input and the nitrogen input. The bromine input is
considered to be originated from bromine-substituted methane. The organic bromine input applied to
the recent model is assumed to be a mixing emission of HOBr and Br2 , whose composition does not
apply much influence on the ODE. Bromine input enhances the ODE by reactivating inert Br beneath
the ice/snow surface, and provides initial Br for the catalytic reaction cycle to consume ozone. There is
a positive correlation between the bromine input and the reducing effect on duration of the induction
stage, while the depletion stage is not significantly affected. For an average level of bromine input,
the induction stage lasts for 3.2 days, which is 1.2 days shorter than that under no organic source input.
The vast majority of the nitrogen input is NO emitted by various plants. NO input has an
enhancement to the ODE, yet not as great as the bromine input. The induction stage is reduced for
a negligible level of 0.2 days, mainly because of the bromine released by heterogeneous reactions.
Changes in organic N input level leads to influence on the chemistry after the atmospheric Br
stability. High organic N input causes transformation from HBr to BrNO2 . When the NO flux
reaches 1.5 × 108 molec./(cm2 ·s), BrNO2 becomes major atmospheric bromine, replacing HBr.
Acknowledgments: Thanks should be given to the financial supports from the National Natural Science
Foundation of China (No. 41375044), the Natural Science Foundation of Jiangsu Province (No. 2015s042),
the Double Innovation Talent Program (No. R2015SCB02), the Polar Strategic Foundation (No. 20150308) and the
Startup Foundation for Introducing Talent of NUIST (No. 2014r066).
Author Contributions: Zhaohuan Liu made the estimation of fluxes from organic sources, and conducted most of
the analyzing and writing job; Le Cao accomplished the work in building up the chemistry reaction mechanism,
calculating the heterogeneous reaction rates, and specifying the inorganic sources.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
The following abbreviations are used in this manuscript:
ODE
PAN
DOM
Ozone Depletion Event
Peroxyacetyl Nitrate
Dissolved Organic Matter
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
Solberg, S.; Schmidbauer, N.; Semb, A.; Stordal, F.; Øystein, H. Boundary-layer ozone depletion as seen in
the Norwegian Arctic in spring. J. Atmos. Chem. 1996, 23, 301–332.
Oltmans, S.; Samuel, J. Surface ozone measurements in clean air. J. Geophys. Res. Oceans 1981, 86, 1174–1180.
Bottenheim, J.; Gallant, A.G.; Brice, K.A. Measurements of NOy species and O3 at 82◦ N latitude.
Geophys. Res. Lett. 1986, 13, 113–116.
Frieß, U.; Hollwedel, J.; König-Langlo, G.; Wagner, T.; Platt, U. Dynamics and chemistry of tropospheric
bromine explosion events in the Antarctic coastal region. J. Geophys. Res. Atmos. 2004, 109, 6305.
Wagner, T.; Ibrahim, O.; Sinreich, R.; Frieß, U.; Glasow, R.V. Enhanced tropospheric BrO over Antarctic sea
ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern. Atmos. Chem. Phys. 2007,
7, 3129–3142.
Helmig, D.; Oltmans, S.; Carlson, D.; Lamarque, J.F.; Jones, A.E. A review of surface ozone in the polar
regions. Atmos. Environ. 2007, 41, 5138–5161.
Helmig, D.; Boylan, P.; Johnson, B.; Oltmans, S.; Fairall, C.; Staebler, R.; Weinheimer, A.; Orlando, J.;
Knapp, D.J.; Montzka, D.D.; et al. Ozone dynamics and snow-atmosphere exchanges during ozone depletion
events at Barrow, Alaska. J. Geophys. Res. Atmos. 2012, 117, 20303.
Jones, A.E.; Anderson, P.S.; Wolff, E.W.; Turner, J.; Rankin, A.M.; Colwell, S.R. A role for newly forming sea
ice in springtime polar tropospheric ozone loss? Observational evidence from Halley station, Antarctica.
J. Geophys. Res. Atmos. 2006, 111, 8306.
Jones, A.E.; Anderson, P.S.; Begoin, M.; Brough, N.; Hutterli, M.A.; Marshall, G.J.; Richter, A.; Roscoe, H.K.;
Wolff, E.W. BrO, blizzards, and drivers of polar tropospheric ozone depletion events. Atmos. Chem. Phys.
2009, 9, 4639–4652.
12
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
Jones, A.E.; Anderson, P.S.; Wolff, E.W.; Roscoe, H.K.; Richter, A.; Brough, N.; Colwell, S.R. Vertical
structure of Antarctic tropospheric ozone depletion events: Characteristics and broader implications.
Atmos. Chem. Phys. 2010, 10, 7775–7794.
Daniel, J.S.; Solomon, S.; Portmann, R.W.; Garcia, R.R. Stratospheric ozone destruction: The importance of
bromine relative to chlorine. J. Geophys. Res. Atmos. 1999, 104, 23871–23880.
Cao, L.; Sihler, H.; Platt, U.; Gutheil, E. Numerical analysis of the chemical kinetic mechanisms of ozone
depletion and halogen release in the polar troposphere. Atmos. Chem. Phys. 2014, 14, 3771–3787.
Fan, S.M.; Jacob, D.J. Surface ozone depletion in Arctic spring sustained by bromine reactions on aerosols.
Nature 1992, 359, 522–524.
Stutz, J.; Platt, U. Improving long-path differential optical absorption spectroscopy with a quartz-fiber mode
mixer. Appl. Opt. 1997, 36, 1105–1115.
Tanner, D.J.; Jefferson, A.; Eisele, F.L. Selected ion chemical ionization mass spectrometric measurement of
OH. J. Geophys. Res. Atmos. 1997, 102, 6415–6425.
Sander, R., Crutzen, P.J. Model study indicating halogen activation and ozone destruction in polluted air
masses transported to the sea. J. Geophys. Res. Atmos. 1996, 101, 9121–9138.
Sander, R.; Vogt, R.; Harris, G.W.; Crutzen, P.J. Modelling the chemistry of ozone, halogen compounds, and
hydrocarbons in the arctic troposphere during spring. Tellus Ser. B 1997, 49, 522–532.
Lehrer, E.; Hönninger, G.; Platt, U. A one dimensional model study of the mechanism of halogen liberation
and vertical transport in the polar troposphere. Atmos. Chem. Phys. 2004, 4, 2427–2440.
Saiz-Lopez, A.; Plane, J.M.C.; Mahajan, A.S.; Anderson, P.S.; Bauguitte, S.J.-B.; Jones, A.E.; Roscoe, H.K.;
Salmon, R.A.; Bloss, W.J.; Lee, J.D.; et al. On the vertical distribution of boundary layer halogens over coastal
Antarctica: Implications for O3 , HOx , NOx and the Hg lifetime. Atmos. Chem. Phys. 2008, 8, 887–900.
Bott, A.; Trautmann, T.; Zdunkowski, W. A numerical model of the cloud-topped planetary boundary layer:
Radiation, turbulence and spectral microphysics in marine stratus. Q. J. R. Meterolog. Soc. 1996, 122, 635–667.
Piot, M.; Glasow, R. The potential importance of frost flowers, recycling on snow, and open leads for ozone
depletion events. Atmos. Chem. Phys. 2008, 8, 2437–2467.
Thomas, J.L.; Stutz, J.; Lefer, B.; Huey, L.G.; Toyota, K.; Dibb, J.E.; Glasow, R.V. Modeling chemistry in and
above snow at Summit, Greenland-Part 1: Model description and results. Atmos. Chem. Phys. 2011, 11,
4899–4914.
Thomas, J L.; Dibb, J.E.; Huey, L.G.; Liao, J.; Tanner, D.; Lefer, B.; Glasow, R.V.; Stutz, J. Modeling chemistry
in and above snow at Summit, Greenland-Part 2: Impact of snowpack chemistry on the oxidation capacity of
the boundary layer. Atmos. Chem. Phys. 2012, 12, 6537–6554.
Foster, K.L; Plastridge, R.A.; Bottenheim, J.W.; Shepson, P.B.; Finlayson-Pitts, B.J.; Spicer, C.W. The role of Br2
and BrCl in surface ozone destruction at polar sunrise. Science 2001, 291, 471–474.
Zeng, T.; Wang, Y.; Chance, K.; Browell, E.V.; Ridley, B.A.; Atlas, E.L. Widespread persistent near-surface
ozone depletion at northern high latitudes in spring. Geophys. Res. Lett. 2003, 30, 2298.
Yang, X.; Cox, R.A.; Warwick, N.J.; Pyle, J.A.; Carver, G.D.; O’Connor, F.M.; Savage, N.H. Tropospheric
bromine chemistry and its impacts on ozone: A model study. J. Geophys. Res. Atmos. 2005, 110, 23311.
Zhao, T.L.; Gong, S.L.; Bottenheim, J.W.; McConnell, J.C.; Sander, R.; Kaleschke, L.; Richter, A.; Kerkweg, A.;
Toyota, K.; Barrie, L.A. A three-dimensional model study on the production of BrO and Arctic boundary
layer ozone depletion. J. Geophys. Res. Atmos. 2008, 113, 24304.
Michalowski, B.A.; Francisco, J.S.; Li, S.M.; Barrie, L.A.; Bottenheim, J.W.; Shepson, P.B. A computer model
study of multiphase chemistry in the Arctic boundary layer during polar sunrise. J. Geophys. Res. Atmos.
2000, 105, 15131–15145.
Sander, R.; Burrows, J.; Kaleschke, L. Carbonate precipitation in brine-a potential trigger for tropospheric
ozone depletion events. Atmos. Chem. Phys. 2006, 6, 4653–4658.
Yang, X.; Pyle, J.A.; Cox, R.A.; Theys, N.; Van Roozendael, M. Snow-sourced bromine and its implications
for polar tropospheric ozone. Atmos. Chem. Phys. 2010, 10, 7763–7773.
Turányi, T. KINAL—A program package for kinetic analysis of reaction mechanisms. Comput. Chem. 1990,
14, 253–254.
Stull Roland, B. An Introduction to Boundary Layer Meteorology; Springer Science & Business Media, 2012;
Volume 13.
13
The 1st International Electronic Conference on Atmospheric Sciences (ECAS 2016), 16–31 July 2016;
Sciforum Electronic Conference Series, Vol. 1, 2016
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
Cao, L.; Platt, U.; Gutheil, E. Role of the boundary layer in the occurrence and termination of the tropospheric
ozone depletion events in polar spring. Atmos. Environ. 2016, 132, 98–110.
Carpenter, L.J.; Liss, P.S. On temperate sources of bromoform and other reactive organic bromine gases.
J. Geophys. Res. Atmos. 2000, 105, 20539–20547.
Manley, S.L.; Goodwin, K.; North, W.J. Laboratory production of bromoform, methylene bromide, and
methyl iodide by macroalgae and distribution in nearshore southern California waters. Limnol. Oceanogr.
1992, 37, 1652–1650.
Cota, G.F.; Sturges, W.T. Biogenic bromine production in the Arctic. Mar. Chem. 1997, 56, 181–192.
Hill, V.L.; Manley, S.L. Release of reactive bromine and iodine from diatoms and its possible role in halogen
transfer in polar and tropical oceans. Limnol. Oceanogr. 2009, 54, 812–822.
Thompson, C.R.; Shepson, P.B.; Liao, J.; Huey, L.G.; Cantrell, C.; Flocke, F.; Orlando, J. Bromine atom
production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska.
Atmos. Chem. Phys. Discuss. 2016, 1–42, doi:10.5194/acp-2015-1039 .
Epstein, H.E.; Calef, M.P.; Walker, M.D.; Chapin, F.S., III; Starfield, A.M. Detecting changes in arctic tundra
plant communities in response to warming over decadal time scales. Glob. Chang. Biol. 2004, 10, 1325–1334.
Nordmeyer, T.; Wang, W.; Ragains, M.L.; Finlayson-Pitt, B.; Spicer, C.W.; Plastridge, R.A. Unique products of
the reaction of isoprene with atomic chlorine: Potential markers of chlorine atom chemistry. Geophys. Res. Lett.
1997, 24, 1615–1618.
Chapin, F.S., III; Shaver, G.R.; Giblin, A.E.; Nadelhoffer, K.J.; Laundre, J.A. Responses of arctic tundra to
experimental and observed changes in climate. Ecology 1995, 76, 694–711.
Walker, D.A.; Raynolds, M.K.; Danils, F.J.A.; Einarsson, E.; Elvebakk, A.; Gould, W.A.; Katenin, A.E.; Kholod,
S.S.; Markson, C.J.; Melnikov, E.S.; et al. The circumpolar Arctic vegetation map. J. Veg. Sci. 2005, 16, 267–282.
Tischner, R.; Planchet, E.; Kaiser, W.M. Mitochondrial electron transport as a source for nitric oxide in the
unicellular green alga Chlorella sorokiniana. FEBS Lett. 2004, 576, 151–155.
Cota, G.F.; Prinsenberg, S.J.; Bennett, E.B.; Loder, J.W.; Lewis, M.R.; Anning, J.L.; Watson, N.H.F.; Harris, L.R.
Nutrient fluxes during extended blooms of Arctic ice algae. J. Geophys. Res. Oceans 1987, 92, 1951–1962.
Ryerson, T.B.; Trainer, M.; Angevine, W.M.; Brock, C.A.; Dissly, R.W.; Fehsenfeid, F.C.; Frost, G.J.; Goldan, P.D.;
Holloway, J.S.; Hubler, G.; et al. Effect of petrochemical industrial emissions of reactive alkenes and NOx on
tropospheric ozone formation in Houston, Texas. J. Geophys. Res. Atmos. 2003, 108, doi:10.1029/2002jd003070.
c 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
14